The present invention relates to semiconductor devices, and more particularly to a method and system for avoiding the build up of a polymer during a plasma etch of an intermetal dielectric when deprocessing the semiconductor device.
FIG. 1 depicts a conventional method 10 for deprocessing a semiconductor device in order to investigate failures in semiconductor devices. Deprocessing removes portions of the semiconductor device to expose structures that are to be studied to determine whether a fault exists and, if so, the type of the fault. The conventional method 10 is described in conjunction with the semiconductor device 30 depicted in FIGS. 2A and 2B. Referring to FIG. 1, a top portion of the semiconductor device is thus removed to expose the intermetal dielectric layer, via step 12. The top portion of the semiconductor device may be mechanically removed or removed in another way. The intermetal dielectric layer exposed is a lower level, such as the intermetal dielectric one layer. The intermetal one dielectric layer insulates the first layer of metal (xe2x80x9cmetal 1xe2x80x9d) from the remainder of the semiconductor device. FIG. 2A depict the semiconductor device 30 after the intermetal dielectric layer 32 has been exposed in step 12. The semiconductor device 30 also includes a local interconnect 34 and a word line 36 above a substrate 31. The local interconnect 34 is included in the first metal layer.
In general, a reactive ion etch and more particularly an anisotropic plasma etch of the intermetal dielectric is performed at an angle perpendicular to the surface of the semiconductor device. However, in practice the plasma etches in an oblique angle, via step 14. An oblique angle is an angle that is greater than zero and smaller than 90 degrees from normal to the surface of the semiconductor device 30. Thus, the direction of the plasma etch is depicted by the arrow 38 in FIG. 2A. An oblique angle is caused by the magnets inside the system below the semiconductor device 30. The investigation of the exposed components and subsequent deprocessing can then be performed, via step 16.
FIG. 2B depicts the semiconductor device 30xe2x80x2 after the plasma etch is performed in step 14. The intermetal dielectric 32 has been removed and thus is not present in FIG. 2B. Most of the word line 36xe2x80x2 and the local interconnect 34xe2x80x2 have been exposed. In addition, a material 40 and 42 has built up on the side of the local interconnect 34xe2x80x2 and the word line 36xe2x80x2g respectively, that were shadowed from the direction of the plasma etch. The material 40 and 42 typically includes a polymer. The material 40 and 42 is due to the plasma etch of the intermetal dielectric 32.
Although the method 10 allows the semiconductor device 30 to be deprocessed, one of ordinary skill in the art will readily realize that the method 10 results in the build up of the material 40 and 42, described above. The material 40 and 42 may cover some or all of the sides of the local interconnect 34xe2x80x2 and the word line 36xe2x80x2. In addition, the material may extend between the local interconnect 34xe2x80x2 and the word line 36xe2x80x2. Because the material 40 and 42 covers at least a portion of the sides of the local interconnect 34xe2x80x2 and the word line 36xe2x80x2g respectively, any faults at the sides of these local interconnect 34xe2x80x2 and the word line 36xe2x80x2 will remain hidden. Similarly, a short between the local interconnect 34xe2x80x2 or the word line 36xe2x80x2 and another structure may be hidden by the material 40 and 42, respectively. Thus, the method 10 may miss some defects in the semiconductor device 30.
Accordingly, what is needed is a system and method for deprocessing semiconductor devices, particularly at lower layers that allows faults to be uncovered. The present invention addresses such a need.
The present invention provides a method and system for deprocessing a semiconductor device. The semiconductor device has a plurality of structures and an intermetal dielectric layer. The method and system comprise anisotropic plasma etching the intermetal dielectric layer at an oblique angle and rotating the semiconductor device during the plasma etch to reduce or eliminate build up of a material on the plurality of structures due to the plasma etch of the intermetal dielectric layer. In another aspect the method and system include a semiconductor device deprocessed using the method in accordance with the present invention. In another aspect, the present invention comprises a system for deprocessing the semiconductor device. The system includes a chamber having a cavity therein for retaining the semiconductor device during a plasma etch of the intermetal dielectric layer. The system also includes a sample holder, coupled with the chamber, for holding the semiconductor device in the chamber and at least one magnet disposed outside of the chamber. In such a system the sample holder is capable of rotating the semiconductor device during the plasma etch to reduce or eliminate build up of a material on the plurality of structures due to the plasma etch of the intermetal dielectric layer without rotating the at least one magnet.
According to the system and method disclosed herein, the present invention allows a semiconductor device to be deprocessed while reducing the build up of a material during deprocessing.